Process for cooling gases



1935- s. HANDFORTH 2,019,533

PROCESS FOR COOLING GASES Filed 001:. 27, 1931 3 Sheets-Sheet l i 1 o [a 11 In i 3 I N VEN TOR.

fimz o4 hand aim BY M A TTORNE Y.

v. 5, 1935- s. L. HANDFORTH 2,019,533

PROCESS FOR COOLING GASES V Filed Oct. 27, 1931 I 3 Sheets-Sheet 2 Fig.2

INVENTOR.

A TTORNEY.

Nov. 5, 1935. s HANDFORTH 2,0195533 PROCESS FOR COOLING GASE S Filed Oct. 27, 1931 3 Sheets-Sheet 3 ATTORNEY.

Patented Nov. 5, 1935 UNITED STATES PATENT OFFICE PROCESS FOR, COOLING GASES Stanley L. Handforth, Woodbury, N. 1., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application October 27, 1931, Serial No. 571,349 10 Claims. (01. 257-224) This invention relates to a process for cooling gases. It relates particularly to an improved process for cooling gases and condensing a vapor therefrom; and more particularly to an improved process for cooling the reaction product from oxidizing ammonia to oxides of nitrogen and condensing therefrom the water and some of the acid formed in the reaction. Still more particularly, it relates to such above processes when they are carried out at pressures greater than atmospheric.

Previous to the present invention, when cool- .ing gases by means of an external cooling fluid,

the gases have been circulated through tubes or nestsof tubes or similar devices, over which a cooling fluid was passed. Particularly in the process of oxidizing ammonia to oxides of nitrogen, the ammonia and oxygen containing gases are passed through a catalyst, where reaction occurs to form oxides of nitrogen and water vapor at a high temperature which in addition are diluted with a large proportion of the inert gas originally present. This hot gas then has to be cooled to the lowest temperature possible with the cooling fluids available. Heretofore, this has been done by passing the gas through pipes or tubular type c'bolers over which the cooling fluid flowed. Under these conditions, the heat transfer rate seldom exceeded 25 B'I'U's per square foot per degree Fahrenheit per hour unless excessive velocities were used with resulting excessive pressure and power losses. This, therefore, required large surfaces and complicated design, and resulted in many structural difliculties.

In certain other dehumidification and solvent recovery processes, the gases have been passed through liquid sprays or other scrubbing equipment and the liquid circulated over cooling coils. This necessitates complicated equipment and under these conditions the rate of heat transfer is of low order.

An object of this invention is to provide a process for cooling gases and condensing a vapor therefrom in a direct and simple manner with the minimum of simple equipment and the maximum use of the surfaces available. A still further object of this invention is the method of accomplishing the above results with apparatus simple and inexpensive to construct and easy to repair and which will introduce the minimum of pressure and power loss in the system.

These objects are accomplished by passing the gases upwardly through a vessel in which is a series of bubbler plates These plates are arranged so that liquid collects to a predetermined depth on these plates and overflows through down pipes to the plate below. The gas passing up through these bubbler plates or permeable diaphragms 3 bubbles through the liquid col- 5 lected thereon and carries some of the liquid upward from plate to plate. Vertical tubes 4 pass completely through this assembly and the cooling fluid is'supplied to the top of these and to the top of the outside of the shell in such a man- 10 ner that it flows in a film down the inside of these tubes and the outside of the shell. In this way a very rapid rate transfer of heat is obtained from the cooling fluid to the walls of the equipment and from the equipment to the liquid 15 collected on the plates or trays within the shell, which liquid is well agitated and splashed against these walls by the gas passing through. The rate of heat. transfer from the liquid to the gas passing through it is also extremely high. 20 I The liquid condensed from the gas may be withdrawn from the desired tray of the coolercondenser through a suitable siphon arrangement which maintains the proper amount of liquid in the apparatus. In case it is desirable 25 to cool a gas which does not contain a condensable liquid it is entirely possible to add liquid directly to the trays so as to maintain the desired amount of liquid in the equipment.

In the oxidation of ammonia to oxides of ni- 30 trogen and nitric acid it is customary to pass a mixture of ammonia and an oxygen containing gas through a catalyst. Reaction takes place and the ammonia is oxidized to oxides of nitrogen, water and some free nitrogen. The heat of re- 35 action raises the temperature of these gases so that they normally leave the converter at from 500 C. to 900 C. These may then be used in a heat exchanger for heating other gases or in a waste heat boiler which may reduce their temperature to as low as C. to 300 C. But in order to carry out the subsequent steps, these gases must be cooled to as low a temperature as possible with the cooling medium available and the water vapor condensed from the gas.

In accordance with the present invention, Figure 1 shows a vertical sectional view of one form of apparatus for carrying out this process in which the cooling tubes pass vertically through 50 the apparatus and the cooling medium can then flow in the form of a film down the inside of these tubes.

Figure 2 shows a partial sectional elevation of another form in which the tubes conducting the 55 cooling medium are in the form offlat coils ;in the pools of liquid. p Q

.-Figure 3 is a view of an enlarged fragmentary .portion of Figure 1 illustrating the fllm of cooling medium flowing down the inner walls of the vertical tubes as well as the exterior of the shell.

Figure 1 illustrates one embodiment of this invention which can be used when this process is carried out at pressures higher than atmospheric. The hot gas from the converters enters shell I, through pipe 2 and leaves through pipe ll. Within shell I is a series of perforated plates 3, and vertical cooling tubes 4, liquid condensed from the gas collects on the perforated plates or trays 3 and the velocity of gas upward through the holes in the plates prevents the liquid draining down through the plates. These are so placed and velocities so regulated that a small amount of liquid will be carried up from plate to plate as spray. The down pipes, 5, return the liquid to the plate below, thus maintaining a constant level of liquidon these plates while the equipment is in operation. Cooling medium is supplied through pipes 6 in such a way that itflows in a film downward through the tubes and around the shell of the cooler. In this way the coldest gas leaving the cooler is in contact with the coldest cooling fluid and the hot gas entering the cooler is in contact with the cooling fluid after it has absorbed heat in the upper parts of the cooler.

uid is agitated by gas bubbling through it and thrown against the surfaces of the cooler so as to continuously wet all these surfaces with a rapidly moving fllm which gives up its heat rapidly to the walls. The cooling medium flowing in a fllm down the walls quickly absorbs the heat.

The liquid condensed from the gas may be withdrawn through pipe I which is in the form of an overflow so as to hold the desired amount of liquid in the cooler. This is vented through pipe 8 to the top of the cooler so as to obtain an even flow. By this means it is possible to withdraw from the cooler a condensate containing a minimum of nitric acid which is extremely desirable in some installations of the process. If it is desirable to obtain a condensate containing a maximum amount of nitric acid, pipe I may be shut off by valve 1' and the liquid removed from the upper tray of the cooler through valve 9 which is then connected to a vent pipe, 8, so as to maintain the proper liquid conditions within the cooler. The piping is so arranged that the liquid does not drain from the cooler when shut down but collects in the lower sections. On starting out, the gas passing through soon carries it upward and distributes it evenly on all the trays.

It will be apparent from the foregoing that many modifications of this equipment may be made. For example Figure 2 shows one modification in which the pipes through which the cooling fluid passes may be coils placed in the liquid on each tray with the ends passing out through the shell instead of vertical pipes as described above. It will also be apparent that trays containing liquid-sealed bubbler caps may be used instead of the perforated plates as described.

This method of cooling is also applicable to other processes in which a gas is being cooled and a condensable vapor removed therefrom. It

, may be used even where no condensable vapor is being removed but liquid may be supplied to the cooler to maintain the desired quantity in the apparatus. As there are many possible modi- The gas passing through the liquid quickly gives up itsheat to the liquid. The liqaorasas flcations of this process and many applications which may be made of it I do not limit myself to the foregoing examples except as indicated in the following claims.

I claim: 5 1. An apparatus for cooling gases, comprising a series of superimposed chambers adapted to receive and discharge the gases, an inlet for the gases near the lowermost of said chambers, an outlet for the gases near the uppermost of said 10 chambers, aseries of permeable diaphragms separating the chambers and adapted to form pools of liquid in the chambers, said pools being in spaced relation and arranged to cause some entrainment of liquid from each pool to the pool 15 next above, overflow means from each pool to the pool below so as to maintain the depth of said pools substantially constant, and a series of tubes passing through the chambers adapted to contain a cooling medium for cooling the liquid 20 which in turn cools the gases.

2. The apparatus of claim 1 in which the tubes pass vertically through said pools and chambers and the cooling medium flows in a fllm under the action of gravity down the walls of the tubes 25 and chambers.

3. An apparatus for cooling gases and condensing vapors therefrom comprising a series of superimposed chambers adapted to receive and discharge the gases, an inlet for the gases near 30 the lowermost of said chambers, an outlet for the gases near the uppermost of said chambers, superimposed permeable diaphragms therein separating the chambers and adapted to form and support pools of liquid in the chambers through which the gases bubble, said pools being in spaced relation and arranged to permit some liquid to be carried upwardly from pool to pool, trapped overflow means for returning the excess liquid to each next lower pool so as to maintain the 40 level in each pool substantially constant, trapped and vented overflow means from at least one of said pools for the removal of accumulated liquid so as to maintain the desired liquid level therein, and a series of tubes passing through the cham- 45 bers adapted to contain a cooling medium for cooling the liquid and the gases.

4. The apparatus of claim 1 in which the tubes pass vetrically through said pools and chambers, and the cooling medium flows in am film under the action of gravity down the walls of the tubes and chambers.

5. The process of cooling a gas which comprises passing the gas through a series of superimposed pools of liquid, transposing portions of 5 the liquid from one pool to the next above in the form of a mist or spray, maintaining substantially constant liquid level in each pool by returning the excess liquid to the next pool below out of contact with the atmosphere, removing the excess liquid from a selected pool, and maintaining a cooling medium in a temperature lowering relation with the liquid, but out of direct contact therewith, while agitating the liquid in said pools by bubbling the gas therethrough. l 6. The process of cooling a gas and condensing a constituent therefrom, which comprises passeilect a rapid transfer of heat from the cooling monia, which comprises passing the gases liquid to the pools, eflecting agitation oi! the liquid and gas during such cooling, and with drawing from at least one pool a portion of the liquid condensed from the gas.

'7. The process of cooling the gaseous reaction products resulting from the oxidation of ammonia, which comprises passing the gases through superimposed pools of liquid, conducting portions of the liquid from one pool to the next above by the gas in contact therewith, maintaining substantially constant liquid level by returning the excess liquid to the next pool below, passing a cooling fluid through the pools, but not in direct contact therewith, to effect a rapid transfer of heat from the cooling liquid to the pools, eflfecting agitation of the liquid and gas during such cooling, and withdrawing from at least one pool a portion of the liquid condensed from the gas.

8. The process of cooling the gaseous reaction products resulting from the oxidation of amrapid transfer of heat from the cooling liquid to through superimposed pools of liquid, conducting portions of the liquid in the form of a mist or spray from one pool to the next above, maintaining substantially constant liquid level by returning the excess liquid to the next pool below, passing a cooling film through the pools in temperature lowering relation to the mist or spray, but out of direct contact therewith, to efiect a the pools, effecting agitation of the liquid and gas during such cooling, and withdrawing from at least one pool a portion of the liquid condensed from the gas.

9. The processof claim 7 in which the steps are carried out under pressures exceeding atmos-, pheric.

10. The process of claim 8 in which the steps are carried out under pressures exceeding atmospheric.

STANLEY L. HANDFORTH. 

